Color image processing device and color image processing method

ABSTRACT

A color image processing device includes a pre-correction unit, a computation processing unit and a post-correction unit. The pre-correction unit includes a pre-correction circuit which carries out a pre-correction to reverse a highest-order bit of a pixel value on input data of a color component. The pre-correction unit selectively outputs the input data of the color component or the data of the color component pre-corrected by the pre-correction circuit according to the color component. The computation processing unit carries out a prescribed computation processing on the data of the color component output by the pre-correction unit and outputs the data of the color component carried out with the prescribed computation processing. The post-correction unit includes a post-correction circuit which carries out a post-correction to reverse a highest-order bit of a pixel value on the data of the color component output by the computation processing unit. The post-correction unit selectively outputs to a prescribed output destination according to the color component, the data of the color component output by the computation processing unit or the data of the color component post-corrected by the post-correction circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a color image processing deviceprovided in a copying machine, a printer machine, a facsimile machineand a scanner machine or the like. In particular, the present inventionrelates to a color image processing device which carries out a scalingprocessing or a spatial filtering processing of a color image.

2. Description of Related Art

A color image processing device provided in a printer machine and ascanner machine or the like includes an image processing circuit such asa scaling processing circuit for executing a scaling processing and aspatial filtering processing circuit for executing a spatial filteringprocessing on scanned color image data of an original document. Insidethe color image processing device, a pixel value of each data of thecolor image data is expressed by a binary digit. For example, in case ofcolor image data of a L*a*b* color system of eight bits, a pixel valueof data of L* component (0 to 255), which takes only a positive value,is expressed by eight bits. A pixel value of data of an a* component anddata of a b* component (−128 to 127), which takes both a positive valueand a negative value, is expressed by code one bit and value seven bits.

Therefore, in a conventional color image processing device, as shown inFIG. 18, an image processing circuit, which executes a computationprocessing on the color image data of the L*a*b* color system, includestwo computation processing circuits, i.e. a computation processingcircuit 37 and a computation processing circuit 38. The computationprocessing circuit 37 executes a computation processing on the data ofthe color component, which takes only a positive value (the data of theL* component). The computation processing circuit 38 executes acomputation processing on the data of the color component, which takesboth a positive value and a negative value (the data of the a* componentand the b* component). Then, among the color image data of the L*a*b*color system, a selection circuit 39 inputs the data of the L* componentto the computation processing circuit 37 and inputs the data of the a*component and the b* component to the computation processing circuit 38.As described above, the data of the L* component and the data of the a*component and the b* component are processed by two computationprocessing circuits 37 and 38.

Another conventional color image processing device can process data ofeach of color components of color image data of a L*a*b* color system byone computation processing circuit. As shown in FIG. 19, an imageprocessing circuit of the conventional color image processing deviceincludes one computation processing circuit 40 which can process data ofnine bits. The computation processing circuit 40 can process the data ofall of the color components of the data of the L* component of eightbits and the data of the a* component and the b* component expressed bycode one bit and value seven bits. Each of the data of the L* component,the data of the a* component and the data of the b* component is inputto the computation processing circuit 40. In the computation processingcircuit 40, a computation processing such as a scaling processing and aspatial filtering processing is executed on the color image datacomposed of the data of the L* component, the data of the a* componentand the data of the b* component.

However, in the conventional color image processing device shown in FIG.18, the computation processing is executed separately on the data of thecolor component, which takes only a positive value, and the data of thecolor component, which takes both a positive value and a negative value.Therefore, two computation processing circuits, i.e. the computationprocessing circuit 37 and the computation processing circuit 38, arerequired to be provided in the image processing circuit. Thus, there isa drawback that a hardware configuration of the image processing circuitbecomes large.

In the conventional color image processing device shown in FIG. 19, boththe data of the color component, which takes only a positive value, andthe data of the color component, which takes both a positive value and anegative value, can be processed in one computation processing circuit.However, to process both of the above-mentioned data by one computationprocessing circuit, a bit number of the data, which can be processed bythe computation processing circuit 40, is required to be set larger thanthe computation processing circuit 37 or the computation processingcircuit 38. Thus, there is a drawback that in the conventional colorimage processing device shown in FIG. 19, a hardware configuration ofthe image processing circuit becomes large as in the conventional colorimage processing device shown in FIG. 18.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of theabove-described drawbacks. An advantage of the present invention is toprovide a color image processing device and a color image processingmethod which can simplify a hardware configuration of an imageprocessing circuit.

According to an aspect of the present invention, a color imageprocessing device carries out a prescribed image processing on colorimage data composed of data of a plurality of color components. Thecolor image processing device includes a pre-correction unit, acomputation processing unit and a post-correction unit. Thepre-correction unit includes a pre-correction circuit which carries outa pre-correction on input data of a color component to reverse ahighest-order bit of a pixel value. According to the color component,the pre-correction unit selectively outputs the input data of the colorcomponent or the data of the color component pre-corrected by thepre-correction circuit. The computation processing unit executes aprescribed computation processing on the data of the color componentoutput by the pre-correction unit and outputs the data of the colorcomponent executed with the prescribed computation processing. Thepost-correction unit includes a post-correction circuit which carriesout a post-correction on the data of the color component output by thecomputation processing unit to reverse the highest-order bit of thepixel value. According to the color component, the post-correction unitselectively outputs to a prescribed output destination, the data of thecolor component output by the computation processing unit or the data ofthe color component post-corrected by the post-correction circuit.

The prescribed computation processing executed by the computationprocessing unit is a scaling processing which calculates a new pixelvalue by carrying out a computation of interpolation by using aplurality of pixel values.

The prescribed computation processing executed by the computationprocessing unit is a spatial filtering processing which calculates a newpixel value by carrying out a computation of convolution by using aplurality of pixel values and prescribed filtering coefficients.

According to another aspect of the present invention, the color imageprocessing device carries out a prescribed image processing on colorimage data composed of data of a plurality of color components. Thecolor image processing device includes a pre-correction unit, acomputation processing unit, a first post-correction unit and a secondpost-correction unit. The pre-correction unit includes a pre-correctioncircuit which carries out a pre-correction on input data of a colorcomponent to reverse a highest-order bit of a pixel value. According tothe color component, the pre-correction unit selectively outputs theinput data of the color component or the data of the color componentpre-corrected by the pre-correction circuit. The computation processingunit executes a computation processing on the data of the colorcomponent output by the pre-correction unit to calculate a total of aproduct of the plurality of pixel values and the prescribed filteringcoefficients. Then, the computation processing unit outputs the data ofthe color component executed with the computation processing. The firstpost-correction unit includes a post-correction circuit which executes aprescribed computation processing on the data of the color componentoutput by the computation processing unit by using a sum of theprescribed filtering coefficients. According to the color component, thefirst post-correction unit selectively outputs the data of the colorcomponent output by the computation processing unit or the data of thecolor component on which the prescribed computation processing has beencarried out by the post-correction circuit. The second post-correctionunit executes a computation processing to divide the data of the colorcomponent output by the first post-correction unit by a power-of-two andoutputs the data of the color component executed with the computationprocessing to a prescribed output destination.

According to one aspect of the present invention, with respect to thedata of the color component which includes a negative value in anumerical range of the pixel value, the pre-correction unit reverses thehighest-order bit of the pixel value and corrects the numerical range ofthe pixel value to a positive value. Therefore, the color imageprocessing device is not required to include both of the computationprocessing circuit, which executes a computation processing on the dataof the color component that takes only a positive value, and thecomputation processing circuit, which executes a computation processingon the data of the color component that takes both a positive value anda negative value. The color image processing device can include only thecomputation processing circuit, which executes the computationprocessing on the data of the color component that takes only a positivevalue. The pre-correction unit corrects the numerical range of the pixelvalue to a positive value. As a result, since the bit expressing thecode becomes unnecessary, the bit number of the computation processingcircuit does not become large. Thus, the hardware configuration of theimage processing circuit can be simplified.

According to the color image processing device of the present invention,the scaling processing circuit having a simplified hardwareconfiguration can be provided.

According to the color image processing device of the present invention,the spatial filtering processing having a simplified hardwareconfiguration can be provided.

According to the color image processing device of the present invention,since the division by the second post-correction unit becomes abit-shift, the spatial filtering processing circuit having a simplifiedhardware configuration can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a configuration of a color image processingdevice according to an embodiment of the present invention.

FIG. 2 shows an example of a configuration of an image processing unitof a color image processing device according to a first embodiment ofthe present invention.

FIG. 3 is a view relating to a scaling processing of color image data.

FIG. 4 shows an example of a configuration of a computation processingcircuit in a scaling processing circuit.

FIG. 5 shows a pixel value and a filtering coefficient.

FIG. 6 shows an example of a configuration of a computation processingcircuit in a spatial filtering processing circuit.

FIG. 7 shows an example of a configuration of the spatial filteringprocessing circuit of a color image processing device according toanother example of the first embodiment of the present invention.

FIG. 8 shows an example of a configuration of an image processing unitof a color image processing device according to a second embodiment ofthe present invention.

FIG. 9 shows an example of a configuration of an image processing unitof a color image processing device according to another example of thesecond embodiment of the present invention.

FIG. 10 shows a computation equation for finding a pixel value L*1 to beinterpolated.

FIG. 11 shows a computation equation for finding a pixel value L*22executed with a spatial filtering processing.

FIG. 12 shows a computation equation for finding a pixel value A*1 to beinterpolated.

FIG. 13 shows a computation equation for finding a pixel value A*22executed with a spatial filtering processing.

FIG. 14 shows a computation equation for finding a pixel value L*22′executed with a spatial filtering processing.

FIG. 15 shows a computation equation for finding the pixel value L*22executed with the spatial filtering processing.

FIG. 16 shows a computation equation for finding the pixel value A*22′executed with the spatial filtering processing.

FIG. 17 shows a computation equation carried out by a firstpost-correction circuit.

FIG. 18 shows an example of a configuration of a conventional imageprocessing circuit.

FIG. 19 shows an example of a configuration of a conventional imageprocessing circuit.

DETAILED DESCRIPTION OF THE INVENTION

A color image processing device 1 according to a first embodiment of thepresent invention will be described with reference to the drawings. Thecolor image processing device 1 carries out a prescribed imageprocessing such as a scaling processing and a spatial filteringprocessing on color image data composed of data of a plurality of colorcomponents. Further, in the present embodiment, a description will bemade of an example in which the color image processing device 1 isapplied to a copying machine. However, the present invention is notlimited to this example and can be applied to another machine such as acolor facsimile machine.

As shown in FIG. 1, the color image processing device 1 includes acontrol unit (Micro Processing Unit (MPU)) 2, a Random Access Memory(RAM) 3, a Read Only Memory (ROM) 4, a document scanning unit 5, animage processing unit 6, a codec 7, an image memory 8, a printer unit 9,a display unit 10, an operation unit 11 and a Universal Serial Bus (USB)device controller 12. Each of the units 2 through 12 is connected via abus 13 in a manner that a communication can be carried out.

The control unit 2 controls each of the units of the color imageprocessing device 1 in accordance with a control program stored in theROM 4. The RAM 3 functions as a main memory and a working area or thelike of the control unit 2. The ROM 4 stores the control program.

Although not shown in the drawing, the document scanning unit 5 includesa color line sensor, an Analog-to-Digital (A/D) converter and an imageprocessing circuit or the like. The document scanning unit 5 scans colorimage data of an original document and executes an image processing suchas an A/D conversion, a shading correction and a gap/line correction.Then, the document scanning unit 5 outputs color image data of aRed-Green-Blue (RGB) color system executed with the image processing toa prescribed output destination. A pixel value of data of each colorcomponent in the color image data of the RGB color system output fromthe document scanning unit 5 is expressed by eight bits, for example,from 0 to 255, for each of a R component, a G component and a Bcomponent. Further, the document scanning unit 5 can scan monochromeimage data of an original document and, for example, the printer unit 9can print an image of the scanned monochrome image data onto printingpaper. However, in the present embodiment, a description will be made ofa case in which the document scanning unit 5 scans color image data.

As shown in FIG. 2, the image processing unit 6 includes an input imageprocessing circuit 14, a multiplexer 15, a scaling processing circuit16, a spatial filtering processing circuit 17 and an output imageprocessing circuit 18. As shown in the drawing, each of the componentsof the image processing unit 6 is connected via an image bus 19. In casethe document scanning unit 5 scans color image data of an originaldocument by a copying function, the input image processing circuit 14carries out a color space conversion of the color image data of the RGBcolor system, which is output from the document scanning unit 5, intocolor image data of a L*a*b* color system. Then, the input imageprocessing circuit 14 outputs the converted color image data to aprescribed output destination. In case the document scanning unit 5scans color image data of an original document by a Personal Computer(PC) scanner function, the input image processing circuit 14 outputs thecolor image data of the RGB color system, which is output from thedocument scanning unit 5, directly to a prescribed output destination.As described above, the input image processing circuit 14 outputs thecolor image data of the RGB color system, which is output from thedocument scanning unit 5, to a prescribed output destination directly orby converging the color space into the color image data of the L*a*b*color system. Further, in the color image data of the L*a*b* colorsystem which the color space has been converted by the input imageprocessing circuit 14, a pixel value of data of an L* component isexpressed by eight bits, for example, from 0 to 255. In the color imagedata of the L*a*b* color system which the color space has been convertedby the input image processing circuit 14, since data of an a* componentand a b* component includes a negative value in a numerical range of apixel value, the pixel value of the data of the a* component and the b*component is expressed by code one bit and value seven bits, forexample, from −127 to 128.

The multiplexer 15 outputs the color image data of the RGB color systemor the L*a*b* color system to the scaling processing circuit 16 for eachcolor component. The multiplexer 15 is controlled by a control signalfrom the control unit 2. For example, in case the control signal fromthe control unit 2 is “0”, the multiplexer 15 outputs the data of the Rcomponent or the L* component to the scaling processing circuit 16. Incase the control signal from the control unit 2 is “1”, the multiplexer15 outputs the data of the G component or the a* component to thescaling processing circuit 16. In case the control signal from thecontrol unit 2 is “2”, the multiplexer 15 outputs the data of the Bcomponent or the b* component to the scaling processing circuit 16. Thedata of each color component is processed in the scaling processingcircuit 16 and the spatial filtering processing circuit 17 by atime-division.

The scaling processing circuit 16 executes a scaling processing on thecolor image data of the RGB color system or the L*a*b* color systemoutput from the multiplexer 15. The scaling processing circuit 16outputs the color image data of the RGB color system or the L*a*b* colorsystem executed with the scaling processing to the spatial filteringprocessing circuit 17. The scaling processing circuit 16 includes apre-correction circuit 23, a first selection circuit 24, a computationprocessing circuit 25, a post-correction circuit 26 and a secondselection circuit 27. The pre-correction circuit 23 carries out apre-correction to reverse a highest-order bit of the pixel value on thedata of each color component of the color image data of the RGB colorsystem and the data of each color component of the color image data ofthe L*a*b* color system input from the multiplexer 15. The firstselection circuit 24 selectively outputs to the computation processingcircuit 25 according to the color component, the data of the colorcomponent input from the multiplexer 15 or the data of the colorcomponent pre-corrected by the pre-correction circuit 23. Specifically,with respect to the data of the color component (each of the R, G, Bcolor components and the L* component), which does not include anegative value in the numerical range of the pixel value, the data ofthe color component input from the multiplexer 15 is output directly tothe computation processing circuit 25. With respect to the data of thecolor component (the a* component and the b* component), which includesa negative value in the numerical range of the pixel value, the data ofthe color component pre-corrected by the pre-correction circuit 23 isoutput to the computation processing circuit 25. Therefore, thepre-correction circuit 23 and the first selection circuit 24 function asa pre-correction unit which selectively outputs the input data of thecolor component or the data of the color component pre-corrected by thepre-correction circuit 23 according to the color component. The firstselection circuit 24 is controlled by the control signal from thecontrol unit 2. For example, in case the data of the R component, the Gcomponent, the B component and the L* component is input, the controlunit 2 inputs a signal of “0” to the first selection circuit 24. Inaccordance with the input signal of “0”, the first selection circuit 24outputs to the computation processing circuit 25, the data of the Rcomponent, the G component, the B component or the L* component inputfrom the multiplexer 15. In case the data of the a* component or the b*component is input, the control unit 2 inputs a signal of “1” to thefirst selection circuit 24. In accordance with the input signal of “1”,the first selection circuit 24 outputs to the computation processingcircuit 25, the data of the a* component or the b* componentpre-corrected by the pre-correction circuit 23.

The computation processing circuit 25 carries out a scaling processingto be described later on the data of each color component. Thepost-correction circuit 26 carries out a post-correction to reverse ahighest-order bit of the pixel value on the data of each color componentof the color image data of the RGB color system and the data of eachcolor component of the color image data of the L*a*b* color systemoutput from the computation processing circuit 25. The second selectioncircuit 27 selectively outputs to the spatial filtering processingcircuit 17 according to the color component, the data of the colorcomponent output from the computation processing circuit 25 or the dataof the color component post-corrected by the post-correction circuit 26.Specifically, with respect to the data of the color component which doesnot include a negative value in the numerical range of the pixel value,in other words, the color component which is not pre-corrected by thepre-correction circuit 23 (each of the R, G, B color components and theL* component), the data of the color component output by the computationprocessing circuit 25 is output directly to the spatial filteringprocessing circuit 25. With respect to the data of the color componentwhich includes a negative value in the numerical range of the pixelvalue, in other words, the color component which is pre-corrected by thepre-correction circuit 23 (the a* component and the b* component), thedata of the color component post-corrected by the post-correctioncircuit 26 is output to the spatial filtering processing circuit 17.Therefore, the post-correction circuit 26 and the second selectioncircuit 27 function as a post-correction unit which selectively outputsto a prescribed output destination according to the color component, thedata of the color component output by the computation processing circuit25 or the data of the color component post-corrected by thepost-correction circuit 26. The second selection circuit 27 iscontrolled by the control signal from the control unit 2 in the samemanner as the first selection circuit 24.

The spatial filtering processing circuit 17 executes a spatial filteringprocessing on the color image data of the RGB color system or the L*a*b*color system output from the scaling processing circuit 16. The spatialfiltering processing circuit 17 outputs the color image data of the RGBcolor system executed with the spatial filtering processing to amultilevel memory of the image memory 8. The spatial filteringprocessing circuit 17 outputs the color image data of the L*a*b* colorsystem executed with the spatial filtering processing to the codec 7,the multilevel memory of the image memory 8 or the output imageprocessing circuit 18. The spatial filtering processing circuit 17includes a pre-correction circuit 28, a first selection circuit 29, acomputation processing circuit 30, a post-correction circuit 31 and asecond selection circuit 32. The pre-correction circuit 28 functions inthe same manner as the pre-correction circuit 23. The first selectioncircuit 29 functions in the same manner as the first selection circuit24. The post-correction circuit 31 functions in the same manner as thepost-correction circuit 26. The second selection circuit 32 functions inthe same manner as the second selection circuit 27. The computationprocessing circuit 30 carries out a spatial filtering processing to bedescribed later on the data of each color component. Further, an orderof the scaling processing circuit 16 and the spatial filteringprocessing circuit 17 is not limited to the above-mentioned order. Thespatial filtering processing circuit 17 can be provided before thescaling processing circuit 16 and after carrying out the spatialfiltering processing in the spatial filtering processing circuit 17, thescaling processing can be carried out in the scaling processing circuit16.

The output image processing circuit 18 carries out a color spaceconversion processing on the color image data of the L*a*b* color systemoutput from the spatial filtering processing circuit 17 for convertinginto the color image data of an output color system. After carrying outthe color space conversion processing, the output image processingcircuit 18 carries out a binarization processing. The color image dataof the output color system is expressed by four components of Cyan (C),Magenta (M), Yellow (Y) and blacK (K). The color image data of theoutput color system after the binarization processing is expressed byone bit for each component of C, M, Y and K. Binary image data binarizedby the output image processing circuit 18 is output to the codec 7 orthe binary memory of the image memory 8.

As shown in FIG. 1, the codec 7 encodes and decodes image data.Specifically, the codec 7 encodes the color image data of the L*a*b*color system, which is output from the spatial filtering processingcircuit 17 of the image processing unit 6, by the Joint PhotographicExperts Group (JPEG) method. The codec 7 decodes the image data encodedby the JPEG method. The codec 7 encodes the binary image data, which isoutput from the output image processing circuit 18 of the imageprocessing unit 6, by the Modified Huffman (MH), the Modified Read (MR),the Modified Modified Read (MMR), the Joint Bi-level Image Group (JBIG)method or the like. The codec 7 decodes the encoded binary image data.

The image memory 8 includes the multilevel memory, the binary memory andan encoding memory. The multilevel memory stores the color image data ofthe RGB color system or the L*a*b* color system output from the spatialfiltering processing circuit 17 of the image processing unit 6. Thebinary memory stores the binary image data binarized by the output imageprocessing circuit 18. The encoding memory stores the color image dataof the L*a*b* color system encoded by the codec 7.

The printer unit 9 prints an image of the image data retrieved from theimage memory 8 onto prescribed paper. The printer unit 9 can print bothcolor image and monochrome image onto the paper. As a printing method ofthe printer unit 9, for example, various printing methods such as anelectrophotographic method and an inkjet printing method can be used.

The display unit 10 is formed from, for example, a Liquid CrystalDisplay (LCD) provided next to the operation unit 11. The display unit10 displays various pieces of screen information. The operation unit 11includes a ten-key numeric pad for inputting a number of copies, a startkey for instructing to start a copying operation, or the like. The usercarries out various operations from the operation unit 11.

The USB device controller 12 executes a device controller function of aUSB. A USB port 20 is provided to the USB device controller 12. When oneend of a USB cable 21 is connected to the USB port 20, the USB is formedand a communication can be carried out with a client PC 22. The USBdevice controller 12 transfers non-encoded color image data of the RGBcolor system or the like, which is stored in the multilevel memory ofthe image memory 8, to the client PC 22, which is connected in a mannercapable of carrying out the communication as described above.

The above-described color image processing device 1 includes the copyingfunction for scanning color image data of an original document andprinting an image of the scanned color image data onto paper and the PCscanner function for scanning color image data of an original documentand transferring an image of the scanned color image data to the clientPC 22. The color image processing device 1 can execute the scalingprocessing and the spatial filtering processing on the color image dataof the original document scanned when executing the copying function orthe PC scanner function.

With reference to FIG. 2, a description will be made of a processingoperation of the scaling processing circuit 16 when carrying out thescaling processing of the color image data of the L*a*b* color system,which is converted by the input image processing circuit 14 after thescanning process of the document scanning unit 5, and a processingoperation of the spatial filtering processing circuit 17 when carryingout the spatial filtering processing on the color image data processedby the scaling processing circuit 16.

The color image data of the L*a*b* color system, which is converted bythe input image processing circuit 14 after the scanning process of thedocument scanning unit 5, is input to the scaling processing circuit 16for each data of each color component by the multiplexer 15. The data ofthe L* component, which the pixel value is expressed by eight bits, andthe data of the a* component and the b* component, which the pixel valueis expressed by code one bit and value seven bits, are input to thescaling processing circuit 16. In case the data of the L* component isinput to the scaling processing circuit 16, the data of the L* componentis input to the pre-correction circuit 23 and the first selectioncircuit 24. The pre-correction circuit 23 carries out a pre-correctionon the input data of the L* component and outputs the pre-corrected dataof the L* component to the first selection circuit 24. Here, since thedata of the L* component does not include a negative value in thenumerical range of the pixel value, the first selection circuit 24selects the data of the L* component input from the multiplexer 15 andoutputs the selected data of the L* component to the computationprocessing circuit 25. That is, the data of the L* componentpre-corrected by the pre-correction circuit 23 is not output to thecomputation processing circuit 25.

In case of enlarging the color image data of the L*a*b* color system,the computation processing circuit 25 calculates a new pixel value,which generates accompanying an enlargement of the data of each colorcomponent, by a computation of interpolation based on the pixel valuebefore the scaling processing. As shown in FIG. 3, suppose that thereare two adjacent pixel values l*1 and l*2 of the L* component before thescaling processing, and a distance between a position of the pixel valueL*1 to be interpolated between the two adjacent pixel values and aposition of the pixel value l*1 and a distance between the position ofthe pixel value L*1 and a position of the pixel value l*2 arerespectively w1 and w2. Then, in case of enlarging the data of the L*component, the computation processing circuit 25 carries out acomputation of an equation shown in FIG. 10 for finding the pixel valueL*1 to be interpolated.

FIG. 4 shows a configuration of the computation processing circuit 25,which carries out a scaling processing based on the equation shown inFIG. 10. As shown in the drawing, the computation processing circuit 25carries out the computation processing of the equation shown in FIG. 10by multiplying l*1 and w2 in a multiplier X1, multiplying l*2 and w1 ina multiplier X2, adding w1 and w2 in an adder Y1, adding a value outputfrom the multiplier X1 and a value output from the multiplier X2 in anadder Y2 and dividing a value output from the adder Y2 by a value outputfrom the adder Y1 in a divider Z1. The computation processing circuit 25outputs the data of the L* component executed with the scalingprocessing to the post-correction circuit 26 and the second selectioncircuit 27. The post-correction circuit 26 carries out a post-correctionon the data of the L* component output by the computation processingcircuit 25 and outputs the post-corrected data of the L* component tothe second selection circuit 27. Here, since the data of the L*component does not include a negative value in the numerical range ofthe pixel value, the second selection circuit 27 selects the data of theL* component output by the computation processing circuit 25 and outputsthe selected data of the L* component to the spatial filteringprocessing circuit 17. That is, the data of the L* componentpost-corrected by the post-correction circuit 26 is not output to thespatial filtering processing circuit 17.

The data of the L* component input to the spatial filtering processingcircuit 17 is input to the pre-correction circuit 28 and the firstselection circuit 29 in the same manner as the scaling processingcircuit 16. The pre-correction circuit 28 carries out a pre-correctionon the input data of the L* component and outputs the pre-corrected dataof the L* component to the first selection circuit 29. Here, since thedata of the L* component does not include a negative value in thenumerical range of the pixel value, the first selection circuit 29selects the data of the L* component input from the scaling processingcircuit 16 and outputs the selected data of the L* component to thecomputation processing circuit 30. That is, the data of the L* componentpre-corrected by the pre-correction circuit 28 is not output to thecomputation processing circuit 30. The computation processing circuit 30carries out a computation of convolution for finding a weighted averageby multiplying a target pixel and surrounding pixels by appropriatecoefficients (filtering coefficients). As shown in FIG. 5, suppose thatthe pixel value l*22 of the L* component is the target pixel and pixelvalues l*ij (i, j=1, 2, 3) and filtering coefficients mij (i, j=1, 2, 3)are provided. Then, by carrying out a computation of an equation shownin FIG. 11, a pixel value L*22 executed with the spatial filteringprocessing is obtained.

FIG. 6 shows a configuration of the computation processing circuit 30which carries out a spatial filtering processing based on the equationshown in FIG. 11. As shown in the drawing, the computation processingcircuit 30 carries out a computation processing of the equation shown inFIG. 11 by multiplying corresponding l*ij (i, j=1, 2, 3) and mij (i,j=1, 2, 3) in each of multipliers X3 through X11, adding all offiltering coefficients mij (i, j=1, 2, 3) in an adder Y3, adding all ofvalues output from the multipliers X3 through X1 in an adder Y4 anddividing a value output from the adder Y4 by a value output from theadder Y3 in a divider Z2. The computation processing circuit 30 outputsthe data of the L* component executed with the spatial filteringprocessing to the post-correction circuit 31 and the second selectioncircuit 32. The post-correction circuit 31 carries out a post-correctionon the data of the L* component output from the computation processingcircuit 30 and outputs the post-corrected data of the L* component tothe second selection circuit 32. Here, since the data of the L*component does not include a negative value in the numerical range ofthe pixel value, the second selection circuit 32 selects the data of theL* component output by the computation processing circuit 30 and outputsthe selected data of the L* component to the output image processingcircuit 18. That is, the data of the L* component post-corrected by thepost-correction circuit 31 is not output to the output image processingcircuit 18.

Meanwhile, in case the data of the a* component is input to the scalingprocessing circuit 16, the data of the a* component is input to thepre-correction circuit 23 and the first selection circuit 24. Thepre-correction circuit 23 carries out a pre-correction on the data ofthe a* component and outputs the pre-corrected data of the a* componentto the first selection circuit 24. For example, in case a pixel value ofthe a* component is “−45”, the pre-correction circuit 23 reverses “1” ofa highest-order bit of “11010011” expressed by two's complement into“0”. The pixel value of the data of the a* component pre-corrected inthe above-described manner becomes “01010011”, in other words, “83”.That is, by reversing the highest-order bit of the pixel value, thepre-correction circuit 23 adds 128 to the input pixel value and correctsthe numerical range of the pixel value of the a* component, which isfrom −128 to 127, into from 0 to 255. Accordingly, the computationprocessing circuit, which executes the computation processing on thedata that takes both a positive value and a negative value, is notrequired to be provided, and only the computation processing circuit,which executes the computation processing on the data that takes only apositive value, can be provided. Moreover, the pre-correction circuitcorrects the numerical range of the pixel value to a positive value. Asa result, since the bit expressing the code becomes unnecessary, the bitnumber of the computation processing circuit does not become large.Thus, the hardware configuration of the image processing circuit can besimplified. The pre-correction circuit 23 outputs the pre-corrected dataof the a* component to the first selection circuit 24. Here, since thedata of the a* component includes a negative value in the numericalrange of the pixel value, the first selection circuit 24 selects thedata of the a* component output by the pre-correction circuit 23 andoutputs the selected data of the a* component to the computationprocessing circuit 25. That is, the data of the a* component input fromthe multiplexer 15 is not output to the computation processing circuit25.

The computation processing circuit 25 carries out the computationprocessing shown in FIG. 10 on the data of the a* component output bythe first selection circuit 24 in the same manner as the data of the L*component. As shown in FIG. 3, in case pixel values a*1 and a*2 of thea* component are given, considering that 128 is added to an actual valueof the pixel value of the a* component by the pre-correction circuit 24,in the equation shown in FIG. 10, if a*1+128 is substituted in l*1 anda*2+128 is substituted in l*2 and a pixel value to be interpolated isA*1, the equation shown in FIG. 10 becomes a calculation equation shownin FIG. 12.

As shown in FIG. 12, the computation processing circuit 25 calculatesthe pixel value of the a* component in which 128 is added to the pixelvalue to be interpolated. Therefore, the data of the a* componentexecuted with the scaling processing can be input to the post-correctioncircuit 26, and the post-correction circuit 26 can subtract 128 frompixel value of the a* component executed with the scaling processing.The computation processing circuit 25 outputs the data of the a*component executed with the scaling processing to the post-correctioncircuit 26 and the second selection circuit 27.

The post-correction circuit 26 carries out a post-correction on the dataof the a* component output by the computation processing circuit 25. Forexample, in case the pixel value of the a* component is “122”, “1” of ahighest-order bit of “11010011” expressed by a binary digit is reversedto “0”. The pixel value of the a* component post-corrected in theabove-described manner becomes “01010011” expressed by two's complement,in other words, “−6”. That is, by reversing the highest-order bit of thepixel value, the post-correction circuit 26 subtracts 128 from the inputpixel value and calculates the pixel value to be found. That is, thepost-correction circuit 26 returns the numerical range of the pixelvalue of the a* component, which has been corrected by thepre-correction circuit 23 to be from 0 to 255, to the numerical rangefrom −128 to 127. The post-correction circuit 26 outputs thepost-corrected data of the a* component to the second selection circuit27. Here, since the data of the a* component includes a negative valuein the numerical range of the pixel value, the second selection circuit27 selects the data of the a* component output by the post-correctioncircuit 26 and outputs the selected data of the a* component to thespatial filtering processing circuit 17. That is, the data of the a*component output by the computation processing circuit 25 is not outputto the spatial filtering processing circuit 17.

In the spatial filtering processing circuit 17, the data of the a*component is input to the pre-correction circuit 28 and the firstselection circuit 29. The pre-correction circuit 28 carries out apre-correction on the data of the a* component input from the scalingprocessing circuit 16 and outputs the pre-corrected data of the a*component to the first selection circuit 29. Here, since the data of thea* component includes a negative value in the numerical range of thepixel value, the first selection circuit 29 selects the data of thecolor component output by the pre-correction circuit 28 and outputs theselected data of the color component to the computation processingcircuit 30. That is, the data of the a* component input from the scalingprocessing circuit 16 is not output to the computation processingcircuit 30. The computation processing circuit 30 carries out thecomputation processing shown in FIG. 11 on the data of the a* componentoutput by the first selection circuit 29 in the same manner as the dataof the L* component. Here, as shown in FIG. 5, in case a pixel valuea*ij (i, j=1, 2, 3) of the a* component is given, considering that 128is added to an actual value of the pixel value of the a* component bythe pre-correction circuit 28, in the equation shown in FIG. 11, ifa*ij+128 is substituted in l*ij and a pixel value to be found is A*22,the equation shown in FIG. 11 becomes a calculation equation shown inFIG. 13.

As shown in FIG. 13, the computation processing circuit 30 calculatesthe pixel value of the a* component, which 128 is added to the pixelvalue to be found. Therefore, the data of the a* component executed withthe spatial filtering processing can be input to the post-correctioncircuit 31 and the post-correction circuit 31 can subtract 128 from thepixel value of the a* component executed with the spatial filteringprocessing. The computation processing circuit 30 outputs the data ofthe a* component executed with the spatial filtering processing to thepost-correction circuit 31 and the second selection circuit 32. Thepost-correction circuit 31 carries out a post-correction on the data ofthe a* component output by the computation processing circuit 30 andoutputs the post-corrected data of the a* component to the secondselection circuit 32. Here, since the data of the a* component includesa negative value in the numerical range of the pixel value, the secondselection circuit 32 outputs the data of the a* component output by thepost-correction circuit 31 to the output color image processing circuit18. That is, the data of the a* component output by the computationprocessing circuit 30 is not output to the output image processingcircuit 18.

Further, a processing operation of the scaling processing circuit 16 andthe spatial filtering processing circuit 17 for the data of the b*component, which includes a negative value in the numerical range in thesame manner as the data of the a* component, is carried out in the samemanner as the processing operation for the data of the a* component. Thecolor image data of the RGB color system, which the pixel value isexpressed by eight bits, is output to the scaling processing circuit 16for each color component by the multiplexer 15, in the same manner asthe color image data of the L*a*b* color system. Since the data of eachof the R, G, B color components does not include a negative value in thenumerical range of the pixel value, the processing operation of thescaling processing circuit 16 and the spatial filtering processingcircuit 17 for the data of each of the R, G, B color components iscarried out in the same manner as the processing operation for the dataof the L* component.

Next, a description will be made of another example of the color imageprocessing device 1 according to the first embodiment of the presentinvention. In the color image processing device 1 of the other exampleof the first embodiment, only the configuration of the spatial filteringprocessing circuit 17 differs from the color image processing device 1shown in FIG. 1 and FIG. 2. Therefore, for a part that is common withthe color image processing device 1, same reference numeral will beapplied and a description will be omitted. Only a different part will bedescribed.

As shown in FIG. 7, a spatial filtering processing circuit 17A of thecolor image processing device includes a pre-correction circuit 28, afirst selection circuit 29, a computation processing circuit 33, a firstpost-correction circuit 34, a second selection circuit 35 and a secondpost-correction circuit 36. When comparing the spatial filteringprocessing circuit 17A with the spatial filtering processing circuit 17shown in FIG. 2, in the spatial filtering processing circuit 17, thecomputation processing circuit 30, the post-correction circuit 31 andthe second selection circuit 32 are provided after the first selectioncircuit 29. In the spatial filtering processing circuit 17A, thecomputation processing circuit 33, the first post-correction circuit 34,the second selection circuit 35 and the second post-correction circuit36 are provided after the first selection circuit 29.

The computation processing circuit 30 carries out the spatial filteringprocessing based on the equation shown in FIG. 11. The computationprocessing circuit 33 carries out a computation processing on the dataof each of the L*, a*, b* color components for calculating a sum of aproduct of a plurality of pixel values and prescribed filteringcoefficients. The first post-correction circuit 34 carries out aprescribed computation processing on the data of the color componentoutput by the computation processing circuit 33 by using a sum of thefiltering coefficients, which is different from the reversal of thehighest-order bit carried out by the post-correction circuit 31.According to the color component, the second selection circuit 35selectively outputs the data of the color component output by thecomputation processing circuit 33 or the data of the color componentexecuted with the prescribed computation processing by the firstpost-correction circuit 34. Specifically, with respect to the data ofthe color component (each of the R, G, B color components and the L*component), which does not include a negative value in the numeric valueof the pixel value, the data of the color component output by thecomputation processing circuit 33 is output directly to the secondpost-correction circuit 36. With respect to the data of the colorcomponent (the a* component and the b* component), which includes anegative value in the numerical range of the pixel value, the data ofthe color component executed with the prescribed computation processingby the first post-correction circuit 34 is output to the secondpost-correction circuit 36. Therefore, the first post-correction circuit34 and the second selection circuit 35 function as a firstpost-correction unit which selectively outputs according to the colorcomponent, the data of the color component output by the computationprocessing circuit 33 or the data of the color component executed withthe prescribed computation processing by the first post-correctioncircuit 34. The second post-correction circuit 36 carries out acomputation processing for dividing the data of the color componentoutput by the second selection circuit 35 by a power-of-two.

Next, a description will be made of a processing operation of thespatial filtering processing circuit 17A when carrying out a spatialfiltering processing on the color image data of the L*a*b* color system.In case the data of the L* component is input to the spatial filteringprocessing circuit 17A, the data of the L* component is input to thepre-correction circuit 28 and the first selection circuit 29. Thepre-correction circuit 28 carries out a pre-correction on the input dataof the L* component and outputs the pre-corrected data of the L*component to the first selection circuit 29. Here, since the data of theL* component does not include a negative value in the numerical range ofthe pixel value, the first selection circuit 29 selects the data of theL* component input from the scaling processing circuit 16 and outputsthe selected data of the L* component to the computation processingcircuit 33. That is, the data of the L* component pre-corrected by thepre-correction circuit 28 is not output to the computation processingcircuit 33. In case the pixel values l*ij (i, j=1, 2, 3) of the L*component and the filtering coefficients mij (i, j=1, 2, 3) are given,the computation processing circuit 33 carries out a computationprocessing to calculate a sum of a product of a plurality of pixelvalues and prescribed filtering coefficients based on the equation shownin FIG. 14 and calculates the pixel value L*22′.

When comparing the equation shown in FIG. 11 and the equation shown inFIG. 14, in the equation shown in FIG. 11, the pixel value calculated bythe equation shown in FIG. 14 is divided by the sum of the filteringcoefficients. However, in the equation shown in FIG. 14, a division isnot carried out. Therefore, the second post-correction circuit 36carries out a division on the data of the L* component. The computationprocessing circuit 30 outputs the data of the L* component executed withthe computation processing of the equation shown in FIG. 14 to the firstpost-correction circuit 34 and the second selection circuit 35. Thefirst post-correction circuit 34 carries out a prescribed computationprocessing by using the sum of the filtering coefficients on the data ofthe L* component output by the computation processing circuit 33. Then,the first post-correction circuit 34 outputs the data of the L*component executed with the computation processing to the secondselection circuit 35. Here, since the data of the L* component does notinclude a negative value in the numerical range of the pixel value, thesecond selection circuit 35 selects the data of the L* component outputby the computation processing circuit 33 and outputs the selected dataof the L* component to the second post-correction circuit 36. That is,the data of the L* component executed with the prescribed computationprocessing by the first post-correction circuit 34 is not output to thesecond post-correction circuit 36.

The second post-correction circuit 36 executes the computationprocessing shown in FIG. 15 to divide the data of the L* componentoutput by the second selection circuit 35 by a power-of-two.Accordingly, the data of the L* component executed with the spatialfiltering processing is output to the output image processing circuit18.

By setting the filtering coefficients mij so that the sum of thefiltering coefficients mij becomes a power-of-two, the division of theequation shown in FIG. 15 can be carried out by a bit shift. As aresult, the computation processing of the equation shown in FIG. 15 canbe carried out easily. By dividing L*22′ by a value of a power-of-twothat is different from the sum of the filtering coefficients mij, thedata of the L* component, which is executed with the spatial filteringprocessing and which a brightness has been changed, can be output. Forexample, by dividing L*22′ by a value of a power-of-two that is smallerthan the sum of the filtering coefficients mij, the data of the L*component, which has a higher brightness than the data of the L*component divided by the sum of the filtering coefficients mij, can becalculated. By dividing L*22′ by a value of a power-of-two that islarger than the sum of the filtering coefficients mij, the data of theL* component, which has a lower brightness than the data of the L*component divided by the sum of the filtering coefficients mij, can becalculated. As described above, when the data of the L* component isinput to the spatial filtering processing circuit 17A, the computationprocessing of the equation shown in FIG. 14 is carried out in thecomputation processing circuit 33 and the division of the equation shownin FIG. 15 is carried out in the second post-correction circuit 36.

When the data of the a* component is input to the spatial filteringprocessing circuit 17A, the data of the a* component is input to thepre-correction circuit 28 and the first selection circuit 29. Thepre-correction circuit 28 carries out a pre-correction on the data ofthe a* component input from the scaling processing circuit 16 andoutputs the pre-corrected data of the a* component to the firstselection circuit 29. Here, since the data of the a* component includesa negative value in the numerical range of the pixel value, the firstselection circuit 29 selects the data of the color component output bythe pre-correction circuit 28 and outputs the selected data of the colorcomponent to the computation processing circuit 33. That is, the data ofthe a* component input from the scaling processing circuit 16 is notoutput to the computation processing circuit 33. The computationprocessing circuit 33 carries out the computation processing shown inFIG. 14 on the data of the a* component output by the first selectioncircuit 29 in the same manner as the L* component. Here, as shown inFIG. 5, in case the pixel value a*ij (i, j=1, 2, 3) of the a* componentis given, considering that 128 is added to an actual value of the pixelvalue of the a* component in the pre-correction circuit 28, if a*1+128is substituted in l*ij and a pixel value to be found is A*22′, theequation shown in FIG. 14 becomes a calculation equation shown in FIG.16.

As shown in FIG. 16, the computation processing circuit 33 calculates apixel value of the a* component that adds a value, which multiplies 128and the sum of the filtering coefficients, to the value to be found.Therefore, the first post-correction circuit 34 can subtract the value,which multiplies 128 and the sum of the filtering coefficients, from thepixel value of the a* component. The computation processing circuit 33outputs the data of the a* component executed with the computationprocessing of the equation shown in FIG. 16 to the first post-correctioncircuit 34 and the second selection circuit 35.

The first post-correction circuit 34 carries out a prescribedcomputation processing by using the sum of the filtering coefficientsbased on the equation shown in FIG. 17 on the data of the a* componentoutput by the computation processing circuit 33.

The first post-correction circuit 34 outputs the data of the a*component executed with the computation processing of the equation shownin FIG. 17 to the second selection circuit 35. Here, since the data ofthe a* component includes a negative value in the numerical range of thepixel value, the second selection circuit 35 selects the data of the a*component output by the first post-correction circuit 34 and outputs theselected data of the a* component to the second post-correction circuit36. That is, the data of the a* component output by the computationprocessing circuit 33 is not output to the second post-correctioncircuit 36. The second post-correction circuit 36 carries out thecomputation shown in FIG. 15 on the data of the a* component output bythe second selection circuit 35 in the same manner as the L* component.As described above, when the data of the a* component is input to thespatial filtering processing circuit 17A, the computation processingcircuit 33 carries out the computation processing of the equation shownin FIG. 16, the first post-correction circuit 34 carries out thecorrection by carrying out the computation processing of the equationshown in FIG. 17, and the second post-correction circuit 36 carries outthe subtraction of the equation shown in FIG. 15.

Further, the computation processing of the spatial filtering processingcircuit 17A for the data of the b* component, which includes a negativevalue in the numerical range in the same manner as the data of the a*component, is carried out in the same manner as the computationprocessing for the data of the a* component. Moreover, since the data ofeach of the R, G, B color components takes only a positive value, thecomputation processing of the spatial filtering processing circuit 17Afor the data of each of the R, G, B color components is carried out inthe same manner as the computation processing for the data of the L*component.

As described above, in the spatial filtering processing circuit 17A, thecomputation processing circuit 33; the first post-correction circuit 34,the second selection circuit 35 and the second post-correction circuit36 are provided after the first selection circuit 29. Since thecomputation processing carried out by the second post-correction circuit36 is a bit-shift, the configuration of the spatial filtering processingcircuit 17A is simple like the spatial filtering processing circuit 17.

Next, a color image processing device according to a second embodimentof the present invention will be described. In the color imageprocessing device according to the second embodiment, only theconfiguration of the image processing circuit 6 differs from the colorimage processing device 1 shown in FIG. 1 and FIG. 2. In the following,for a part that is common with the color image processing device 1according to the first embodiment, the same reference numeral will beapplied and the description will be omitted. Only a different part willbe described.

The image processing unit 6 described with reference to FIG. 2 includesone scaling processing circuit 16 and one spatial filtering processingcircuit 17 and carries out a processing on the color image data of theRGB color system or the color image data of the L*a*b* color system foreach color component by a time-division. As shown in FIG. 8, an imageprocessing unit 6A of the color image processing device according to thesecond embodiment includes a circuit for carrying out a scalingprocessing and a circuit for carrying out a spatial filtering processingfor each color component. Among the color image data of the RGB colorsystem and the color image data of the L*a*b* color system, the data ofthe L* component and the data of the R* component are configured to beprocessed in the same circuit. Since the data of the L* color componentand the data of the R* component are the data which do not include anegative value in the numerical range of the pixel value, apre-correction or a post-correction is not necessary. After the scalingprocessing is executed by the computation processing circuit 25, thespatial filtering processing is executed by the computation processingcircuit 30. Moreover, the data of the a* component and the data of the Gcomponent are configured to be processed in the same circuit. However,the data of the a* component is the data which includes a negative valuein the numerical range of the pixel value, and the data of the Gcomponent is the data which does not include a negative value in thenumerical range of the pixel value. Therefore, the data of the a*component and the data of the G component are processed in a scalingprocessing circuit 16 a (16), which is the same as the scalingprocessing circuit 16, and a spatial filtering processing circuit 17 a(17), which is the same as the spatial filtering processing circuit 17.Moreover, the data of the b* component and the data of the B componentare configured to be processed in the same circuit as the data of the a*component and the data of the G component. The data of the b* componentand the data of the B component are processed in a scaling processingcircuit 16 b (16), which is the same as the scaling processing circuit16, and a spatial filtering processing circuit 17 b (17), which is thesame as the spatial filtering processing circuit 17.

As described above, the circuit for carrying out the scaling processingand the circuit for carrying out the spatial filtering processing areprovided for each color component. Although the configuration of theimage processing unit 6A becomes large compared with the imageprocessing unit 6, the data of each color component can be processedsimultaneously. Therefore, the color image processing device accordingto the second embodiment can carry out the processing under higher speedcompared with the color image processing device 1 which processes eachcolor component data of the color image data of the RGB color system orthe color image data of the L*a*b* color system by a time-division.

In the image processing unit 6B shown in FIG. 9, the data of the L*component and the data of the R component are configured so that thespatial filtering processing is executed in the computation processingcircuit 33 and the second post-correction circuit 36. In this case,since the data of the L* component and the data of the R component aredata which do not include a negative value in the numerical range of thepixel value, the pre-correction circuit 28, the first selection circuit29, the first post-correction circuit 34 and the second selectioncircuit 35 are unnecessary. The data of the a* component and the data ofthe G component are configured to be processed in a spatial filteringprocessing circuit 17 c (17A), which is the same as the spatialfiltering processing circuit 17A. The data of the b* component and thedata of the B component are configured to be processed in a spatialfiltering processing circuit 17 d (17A), which is the same as thespatial filtering processing circuit 17A.

Further, in the above-described embodiment of the present invention, adescription has been made of a case in which the image processing unit 6carries out the scaling processing and the spatial filtering processing.However, another image processing circuit can be provided and in thesame manner as the image processing unit 6, data with a code and datawithout a code can be processed in the same circuit. In this case, inplace of the computation processing circuit which carries out thescaling processing and the computation processing circuit which carriesout the spatial filtering processing, a computation processing circuitwhich carries out a computation processing corresponding to the imageprocessing can be provided.

In the above-described embodiment of the present invention, adescription has been made of a case in which the scaling processingcircuit 16 and the spatial filtering processing circuit 17 carry out theimage processing on the color image data of the RGB color system and theL*a*b* color system. However, the color space of the color image datainput to the scaling processing circuit 16 and the spatial filteringprocessing circuit 17 is not limited to the above-mentioned colorspaces. For example, color image data of bg-sRGB color system, colorimage data of scRGB color system or color image data of YCrCb colorsystem can be used. In this case, the input image processing circuit 14can be configured to carry out a processing to convert the color imagedata of the RGB color system output from the document scanning unit 5into these color spaces (bg-sRGB color system, scRGB color system andYCrCb color system). In the above-described embodiment, a descriptionhas been made of the image processing for the data of eight bits.However, the image processing can be executed also on the data of 10bits or 12 bits.

1. A color image processing device, comprising: means for inputtingcolor image data including data of a plurality of color components; apre-correcting means which includes a pre-correction circuit thatcarries out a pre-correction to reverse a highest-order bit of a pixelvalue on data of a color component input from the means for inputtingand which selectively outputs the data of the color component input fromthe means for inputting or the data of the color component pre-correctedby the pre-correction circuit according to the color component; acomputation processing means for carrying out a prescribed computationprocessing on the data of the color component output by thepre-correcting means and outputting the data of the color componentcarried out with the prescribed computation processing; and apost-correcting means which includes a post-correction circuit thatcarries out a post-correction to reverse a highest-order bit of a pixelvalue on the data of the color component output by the computationprocessing means and which selectively outputs to a prescribed outputdestination according to the color component, the data of the colorcomponent output by the computation processing means or the data of thecolor component post-corrected by the post-correction circuit.
 2. Thecolor image processing device according to claim 1, wherein theprescribed computation processing carried out by the computationprocessing means is a scaling processing which calculates a pixel valueby carrying out a computation of interpolation by using a plurality ofpixel values.
 3. The color image processing device according to claim 1,wherein the prescribed computation processing carried out by thecomputation processing means is a spatial filtering processing whichcalculates a pixel value by carrying out a computation of convolution byusing a plurality of pixel values and prescribed filtering coefficients.4. The color image processing device according to claim 1, wherein thepre-correcting means outputs the data of the color component input fromthe means for inputting for data of a color component that does notinclude a negative value in a numerical range and outputs the data ofthe color component pre-corrected by the pre-correction circuit for dataof a color component that includes a negative value in the numericalrange; and the post-correcting means outputs the data of the colorcomponent output by the computation processing means to a prescribedoutput destination for the data of the color component that does notinclude a negative value in the numerical range and outputs the data ofthe color component post-corrected by the post-correction circuit to theprescribed output destination for the data of the color component thatincludes a negative value in the numerical range.
 5. The color imageprocessing device according to claim 1, wherein the means for inputtinginputs data expressed by a L*a*b* color system; the pre-correcting meansoutputs the data of the color component input from the means forinputting for data of a L* component and outputs the data of the colorcomponent pre-corrected by the pre-correction circuit for data of an a*component and a b* component; and the post-correcting means outputs thedata of the color component output by the computation processing meansto a prescribed output destination for the data of the L* component andoutputs the data of the color component post-corrected by thepost-correction circuit to the prescribed output destination for thedata of the a* component and the b* component.
 6. The color imageprocessing device according to claim 1, wherein the means for inputtingselectively inputs data expressed by a L*a*b* color system or dataexpressed by a Red-Green-Blue (RGB) color system; the pre-correctingmeans outputs the data of the color component input from the means forinputting for data of a L* component and RGB components and outputs thedata of the color component pre-corrected by the pre-correction circuitfor data of an a* component and a b* component; and the post-correctingmeans outputs the data of the color component output by the computationprocessing means to a prescribed output destination for the data of theL* component and the RGB components and outputs the data of the colorcomponent post-corrected by the post-correction circuit to theprescribed output destination for the data of the a* component and theb* component.
 7. A color image processing device, comprising: means forinputting color image data including data of a plurality of colorcomponents; a pre-correcting means which includes a pre-correctioncircuit that carries out a pre-correction to reverse a highest-order bitof a pixel value on data of a color component input from the means forinputting and which selectively outputs the data of the color componentinput from the means for inputting or the data of the color componentpre-corrected by the pre-correction circuit according to the colorcomponent; a computation processing means for carrying out a computationprocessing to calculate a total of a product of a plurality of pixelvalues and prescribed filtering coefficients on the data of the colorcomponent output by the pre-correcting means and outputting the data ofthe color component carried out with the computation processing; a firstpost-correcting means which includes a post-correction circuit thatcarries out a prescribed computation processing by using a sum of theprescribed filtering coefficients on the data of the color componentoutput by the computation processing means and which selectively outputsthe data of the color component output by the computation processingmeans or the data of the color component executed with the prescribedcomputation processing by the post-correction circuit according to thecolor component; and a second post-correcting means for carrying out acomputation processing to divide the data of the color component outputby the first post-correcting means by a power-of-two and outputting to aprescribed output destination.
 8. The color image processing deviceaccording to claim 7, wherein the pre-correcting means outputs the dataof the color component input from the means for inputting for data of acolor component that does not include a negative value in a numericalrange and outputs the data of the color component pre-corrected by thepre-correction circuit for data of a color component that includes anegative value in the numerical range; and the first post-correctingmeans outputs the data of the color component output by the computationprocessing means to a prescribed output destination for the data of thecolor component that does not include a negative value in the numericalrange and outputs the data of the color component executed with theprescribed computation processing by the post-correction circuit to theprescribed output destination for the data of the color component thatincludes a negative value in the numerical range.
 9. The color imageprocessing device according to claim 7, wherein the means for inputtinginputs data expressed by a L*a*b* color system; the pre-correcting meansoutputs the data of the color component input from the means forinputting for data of a L* component and outputs the data of the colorcomponent pre-corrected by the pre-correction circuit for data of an a*component and a b* component; and the first post-correcting meansoutputs the data of the color component output by the computationprocessing means to a prescribed output destination for the data of theL* component and outputs the data of the color component executed withthe prescribed computation processing by the post-correction circuit tothe prescribed output destination for the data of the a* component andthe b* component.
 10. The color image processing device according toclaim 7, wherein the means for inputting selectively inputs dataexpressed by a L*a*b* color system or data expressed by a Red-Green-Blue(RGB) color system; the pre-correcting means outputs the data of thecolor component input from the means for inputting for data of a L*component and RGB components and outputs the data of the color componentpre-corrected by the pre-correction circuit for data of an a* componentand b* component; and the first post-correcting means outputs the dataof the color component output by the computation processing means to aprescribed output destination for the data of the L* component and theRGB components and outputs the data of the color component executed withthe prescribed computation processing by the post-correction circuit tothe prescribed output destination for the data of the a* component andthe b* component.
 11. A color image processing method, comprising: aninputting step of inputting color image data including data of aplurality of color components; a pre-correcting step of selectivelyoutputting data of a color component input at the inputting step or dataof a color component executed with a pre-correction to reverse ahighest-order bit of a pixel value on the data of the color componentinput at the inputting step according to a color component of data inputat the inputting step; a computation processing step of carrying out aprescribed computation processing on the data of the color componentoutput at the pre-correcting step and outputting the data of the colorcomponent carried out with the prescribed computation processing; and apost-correcting step of selectively outputting to a prescribed outputdestination according to the color component of the data output at thecomputation processing step, the data of the color component output atthe computation processing step or the data of the color componentexecuted with a post-correction to reverse a highest-order bit of apixel value on the data of the color component output at the computationprocessing step.
 12. The color image processing method according toclaim 11, wherein the prescribed computation processing carried out atthe computation processing step is a scaling processing which calculatesa pixel value by carrying out a computation of interpolation by using aplurality of pixel values.
 13. The color image processing methodaccording to claim 11, wherein the prescribed computation processingcarried out at the computation processing step is a spatial filteringprocessing which calculates a pixel value by carrying out a computationof convolution by using a plurality of pixel values and prescribedfiltering coefficients.
 14. The color image processing method accordingto claim 11, wherein at the pre-correcting step, for data of a colorcomponent that does not include a negative value in a numerical range,the data of the color component input at the inputting step is output,and for data of a color component that includes a negative value in thenumerical range, the pre-corrected data of the color component isoutput; and at the post-correcting step, for the data of the colorcomponent that does not include a negative value in the numerical range,the data of the color component output at the computation processingstep is output to a prescribed output destination, and for the data ofthe color component that includes a negative value in the numericalrange, the post-corrected data of the color component is output to theprescribed output destination.
 15. The color image processing methodaccording to claim 11, wherein at the inputting step, data expressed bya L*a*b* color system is input; at the pre-correcting step, among thedata expressed by the L*a*b* color system, for data of a L* component,the data of the color component input at the inputting step is output,and for data of an a* component and a b* component, the pre-correcteddata of the color component is output; and at the post-correcting step,among the data expressed by the L*a*b* color system, for the data of theL* component, the data of the color component output at the computationprocessing step is output to a prescribed output destination, and forthe data of the a* component and the b* component, the post-correcteddata of the color component is output to the prescribed outputdestination.
 16. The color image processing method according to claim11, wherein at the inputting step, data expressed by a L*a*b* colorsystem or data expressed by a Red-Green-Blue (RGB) color system is inputselectively; at the pre-correcting step, for data of a L* component andRGB components, the data of the color component input at the inputtingstep is output, and for data of an a* component and a b* component, thepre-corrected data of the color component is output; and at thepost-correcting step, for the data of the L* component and the RGBcomponents, the data of the color component output at the computationprocessing step is output to a prescribed output destination, and forthe data of the a* component and the b* component, the post-correcteddata of the color component is output to the prescribed outputdestination.
 17. A color image processing method, comprising: aninputting step of inputting color image data including data of aplurality of color components; a pre-correcting step of selectivelyoutputting the data of the color component input at the inputting stepor data of a color component executed with a pre-correction to reverse ahighest-order bit of a pixel value on the data of the color componentinput at the inputting step according to the color component of the datainput at the inputting step; a computation processing step of carryingout a computation processing to calculate a total of a product of aplurality of pixel values and prescribed filtering coefficients on thedata of the color component output at the pre-correcting step andoutputting the data of the color component carried out with thecomputation processing; a first post-correcting step of selectivelyoutputting the data of the color component output at the computationprocessing step or the data of the color component executed with aprescribed computing processing on the data of the color componentoutput at the computation processing step according to the colorcomponent of the data output at the computation processing step; and asecond post-correcting step of carrying out a computation processing todivide the data of the color component output at the firstpost-correcting step by a power-of-two and outputting to a prescribedoutput destination.
 18. The color image processing method according toclaim 17, wherein at the pre-correcting step, for data of a colorcomponent that does not include a negative value in a numerical range,the data of the color component input at the inputting step is output,and for data of a color component that includes a negative value in thenumerical range, the pre-corrected data of the color component isoutput; and at the first post-correcting step, for the data of the colorcomponent that does not include a negative value in the numerical range,the data of the color component output at the computation processingstep is output to a prescribed output destination, and for the data ofthe color component that includes a negative value in the numericalrange, the data of the color component executed with the prescribedcomputation processing is output to the prescribed output destination.19. The color image processing method according to claim 17, wherein atthe inputting step, data expressed by a L*a*b* color system is input; atthe pre-correcting step, among the data expressed by the L*a*b* colorsystem, for data of a L* component, the data of the color componentinput at the inputting step is output, and for data of an a* componentand a b* component, the pre-corrected data of the color component isoutput; and at the first post-correcting step, among the data expressedby the L*a*b* color system, for the data of the L* component, the dataof the color component output at the computation processing step isoutput to a prescribed output destination, and for the data of the a*component and the b* component, the data of the color component executedwith the prescribed computation processing is output to the prescribedoutput destination.
 20. The color image processing method according toclaim 17, wherein at the inputting step, data expressed by a L*a*b*color system or data expressed by a Red-Green-Blue (RGB) color system isinput selectively; at the pre-correcting step, for data of a L*component and RGB components, the data of the color component input atthe inputting step is output, and for data of an a* component and a b*component, the pre-corrected data of the color component is output; andat the first post-correcting step, for the data of the L* component andthe RGB components, the data of the color component output at thecomputation processing step is output to a prescribed outputdestination, and for the data of the a* component and the b* component,the data of the color component executed with the prescribed computationprocessing is output to the prescribed output destination.